Following mod will change the link on intermediate pic so that instead of opening the pop for fullsize pic the user will be taken to the next pic (as if he clicked the Next button).
Edit themes/yourtheme/theme.php (function theme_html_picture) [If that function is not there in your theme then copy it from sample theme to your theme.php]
Replace
global $album, $comment_date_fmt, $template_display_media;
with
global $album, $comment_date_fmt, $template_display_media, $cat, $pos, $pic_count;
then Replace
$pic_html = "<a href=\"javascript:;\" onclick=\"MM_openBrWindow('displayimage.php?pid=$pid&fullsize=1','" . uniqid(rand()) . "','scrollbars=yes,toolbar=no,status=no,resizable=yes,width=$winsizeX,height=$winsizeY')\">";
$pic_title = $lang_display_image_php['view_fs'] . "\n==============\n" . $pic_title;
$pic_html .= "<img src=\"" . $picture_url . "\" class=\"image\" border=\"0\" alt=\"{$lang_display_image_php['view_fs']}\" /><br />";
$pic_html .= "</a>\n";
with
if ($pos < ($pic_count - 1)) {
$next = $pos + 1;
$cat_link = is_numeric($album) ? '' : '&cat=' . $cat;
$pic_html = "<a href=\"{$_SERVER['PHP_SELF']}?album=$album$cat_link&pos=$next$uid_link\">";
}
$pic_title = $lang_display_image_php['view_fs'] . "\n==============\n" . $pic_title;
$pic_html .= "<img src=\"" . $picture_url . "\" class=\"image\" border=\"0\" alt=\"{$lang_display_image_php['view_fs']}\" /><br />";
if ($pos < ($pic_count - 1)) {
$pic_html .= "</a>\n";
}
HTH
Abbas